1. Field of the Invention
This invention relates to a temperature sensing device, a semiconductor device having this temperature sensing device installed therein and an auto-focusing (AF) system using this semiconductor device.
2. Description of Related Art
As one of the applications of a solid-state imaging device, for example, a CCD (Charge Coupled Device) linear sensor, there is provided an auto-focusing sensor (hereinafter called as an AF sensor). In a simple AF sensor, a so-called triangle measuring system is applied for calculating a distance. That is, as shown in FIG. 11, there are provided two lenses 101, 102 spaced apart by a specified distance L and further there are arranged two CCD linear sensors 103, 104 spaced apart by a specified distance (d) in respect to each of these lenses 101, 102.
Then, distances X1, X2 ranging from each of the center points of the lenses 101, 102 to each of image focusing points P1, P2 are calculated in response to each of output signals when an object P is focused on the two CCD linear sensors 103, 104 through the lenses 101, 102, and then a position of each of the lenses 101, 102 in their optical axial directions is automatically controlled so as to satisfy an equation 1 below. EQU D=d.times.{L/(X1+X2)} Equ. 1
In the aforesaid AF sensor, it is generally applied that a plastic lens is normally used as this type of lens in order to make a low cost assembly. However, in recent years, there has been found a tendency that a CCD sensor with a multi-pixel high density characteristic is used in order to manufacture a high precision AF sensor and in this case, an error caused by a variation in strain (aberration) caused by a temperature in an optical system of such a lens as above to be used and the like can not be ignored, resulting in that the error is required to be corrected. Due to this fact, it becomes necessary to provide a temperature sensing device for use in sensing a variation in temperature. In that case, it is advantageous to install the temperature sensing device on a CCD chip in view of its cost and space and the installation on the chip enables a temperature of the AF sensor by itself to be measured accurately, so that its correcting accuracy may also be improved.
As shown in FIG. 12A and FIG. 12B, it is well known to provide this type of temperature sensing device in which a normal electrical current is flowed in a pn-junction diode and a variation of voltage value of a forward direction on-voltage (a turn-on voltage) is utilized. With such an arrangement as above, although a voltage value of the forward direction on-voltage of the pn-junction diode indicates a junction voltage value of about 0.7 V at a normal temperature, this junction voltage value is reduced if the temperature is increased under the same condition (for example, the electrical current is the same) as that of the measurement at the normal temperature in the case of silicon Si. Actually, this variation is about -2 mV/.degree.C. per one piece of diode, so that it is necessary to connect a plurality of stages of diodes (two stages in this example) as shown in FIG. 13A and FIG. 13B or to connect an amplifying circuit having a less dependency of temperature on an amplification rate to a stage subsequent to the former stages in order to attain a high precision sensing of the temperature.
In addition, it is also well known as another temperature sensing device to utilize variation in voltage value of a base-emitter junction voltage V.sub.BE of a bipolar transistor caused by the temperature. However, since the temperature sensing device using the pn-junction diode or the bipolar transistor is naturally realized by a bipolar process, it is difficult to install this device on a CCD linear sensor in view of its manufacturing process. Even if the diode could be installed on a chip, it would be difficult to install a high precision amplifying circuit on the chip.
Further, although it is widely known to perform a temperature sensing with a thermistor, it is necessary to install it on the chip in order to perform an accurate measurement of a measured device. In such a case as one in which the installation on the chip is required, it may not be realized with a thermistor (an element normally called as a thermistor). In view of such reasons as described above, it is desired to develop a temperature sensing device which can be realized by a so-called MOS process.